Paul Johnson wrote:
> On Wed, Mar 12, 2003 at 03:09:36PM -0800, R. Joseph Newton wrote:
> > Mark Anderson wrote:
> >
> > > > It sounds like you need a count hash. You might try something like:
> > > >
> > > > my @tokens = split /:/;
> > > > foreach (@tokens) {
> > > > if ($tokenCount{$_}) {
> > > > $tokenCount{$_}++;
> > > > } else {
> > > > $tokenCount{$_} = 1;
> > > > }
> > > > }
> > >
> > > The following works the same and may or may not be easier to
> > > understand/maintain.
> > > $tokenCount{$_} is automatically created with a value of 0 when first
> > > called, and
> > > then is incremented to 1, so you don't have to test or create it yourself.
> > >
> > > my @tokens = split /:/;
> > > for (@tokens) {
> > > $tokenCount{$_}++
> > > } # for
> >
> > Wow! It works. I'm not sure that's such a good thing, though. How
> > does one ditinguish, then, between 0 as a meaningful value, and a
> > still-undefined variable?
>
> And I'd code that as:
>
> $tokenCount{$_}++ for split /:/;
>
> Well, actually, as:
>
> $token_count{$_}++ for split /:/;
>
> Check for definedness with C<defined $token_count{$token}>
>
> or existence with C<exists $token_count{$token}>
>
> > I think, for the sake of healthy discipline, at least, that I would
> > stick with explicitly assigning a numerical value to my variables
> > before executing any other operations on them. Implicit casts from
> > undef? Boolean--aye, any other type, Nay!
>
> This is actually a common Perl idiom, and very useful in situations such
> as this. Of course, anyone is free to program in any way they please,
> but for me, the longer version is slower to write, slower to read and
> understand and slower to run.
Hi Mark,
Are you a beginner at Perl, as is the original poster? Somehow I doubt it.
If you can show me some benchmarks on the running times that show any serious loss in
performance, I would gladly take that into consideration. I would certainly grant
also, that a seasoned Perl programmer might understand the cryptic syntaces proposed
at a glance. I find that highly unlikely in the case of anyone new to the arcane Perl
argot.
In retrospect, I could have been more clear by using
if (defined ($tokenCount{$_}) {
since this would more clearly communicate that keys already encountered have their
count incremented, whie any previously unseen key is being created and initialized to
1 in one fell swoop.
Since the incrementation think it would be counter-productive to further obscure the
process by trying to crunch it down to some obscure, context-deprived [in spite of the
ready availability of the working context] one-liner.
Joseph
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